The amount of traffic in wireless communication systems is increasing rapidly. A user nevertheless expects high quality communication to be provided and various efforts are made to keep the user satisfaction, for example providing increased throughput by means of MIMO, and by developing different interference limiting strategies.
Multiple-input Multiple-output (MIMO) technology is thus an effort to improve communication performance and offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. In MIMO multiple antennas are used at the transmitter to transmit multiple independent data streams to the receiver. As an example, in dual-stream MIMO, the receiver uses two receive antennas to extract the two data streams, and suppresses one data stream while recovering the other. Under good radio conditions such dual-stream MIMO transmissions can double the user rates. The transmitter typically chooses the number of data streams to transmit based on channel quality feedback received from the receiver. The number of independent transmission streams is called the rank of the signal and the process of selecting the number of streams is called rank adaptation.
Inter-cell interference is a main factor that limits performance cellular wireless communication systems and there are receivers designed to suppress or cancel interference from neighbor cells. In particular, receivers with interference suppression (IS) capabilities are being introduced and may increase user satisfaction. Such receivers use multiple antennas and/or advanced algorithms to suppress interference from transmissions in neighboring cells. The IS receivers provide large gains particularly in cell-edge performance, and a user located close to the cell border and subject to interference from a small number of interference sources has very effective interference suppression when using such IS receiver. It may be assumed that IS receivers are able to remove more than 90% of the interference power from a single interference source. However, this IS efficiency is significantly reduced as multiple interferers need to be cancelled.
As the wireless traffic within the communication system increases, there is a constant strive to find new ways to combat interference and provide improved performance for the increasing number of users.